1. Field of the Invention
The present invention relates to a feedforward amplifier and a feedforward amplification method used for a base station apparatus of mobile communication equipment and so on.
2. Related Art of the Invention
In recent years, a power amplifier of high efficiency and high linearity is required for a transmitter of a base station of mobile communication equipment in order to amplify a large number of signaling channels by one operation, and improvement in the linearity is implemented by performing distortion compensation by a feedforward method.
A feedforward amplifier will not be described in detail here since it is also described in John L. B. Walker, xe2x80x9cHigh-Power GaAs FET Amplifiers,xe2x80x9d Artech House, 1993, pp. 332 to 333, for instance. Moreover, the entire disclosure of this literature are incorporated herein by reference in its entity.
And in recent years, a CDMA (Code Division Multiple Access) method of a broad band is adopted as a modulation method of a portable telephone, so that the base station also requires broad-band transmission, and broad-band distortion compensation control is also required for feedforward distortion compensation. Moreover, the CDMA method will not be described in detail here since it is also described in Nick Pothecary, xe2x80x9cFeedforward Linear Power Amplifiers,xe2x80x9d Artech House, 1999, pp. 73 to 76, for instance. Moreover, the entire disclosure of this literature are incorporated herein by reference in its entity.
The feedforward amplifier of implementing such broad-band control is exemplified by Japanese Patent Laid-Open No. 8-56126 xe2x80x9cDistortion Compensation Amplifier Circuit,xe2x80x9d which will be described by referring to FIG. 3. In FIG. 3, reference numeral 1 denotes a first directional coupler, 2 denotes a first vector adjustor, 3 denotes a main amplifier, 4 denotes a second directional coupler, 5 denotes a first delay element, 6 denotes a second delay element, 7 denotes a second vector adjustor, 8 denotes an auxiliary amplifier, 9 denotes a third directional coupler, 10 denotes an amplifier, 11a denotes a pilot signal generator, 11b denotes a modulation signal generator, 12 denotes a detector, 14 denotes a digital-type control circuit comprised of an A/D converter, a D/A converter, a CPU and a memory, 21 denotes a DSB signal generator comprised of the pilot signal generator 11a and modulation signal generator 11b, and 22 denotes a DSB orthogonal detection circuit comprised of a reference signal generator, an orthogonal mixer, a filter and the A/D converter.
In this configuration, a removal control circuit uses at least two oscillators of the pilot signal generator 11a and modulation signal generator 11b and mixes signals from these two oscillators while rendering the signal from the pilot signal generator 11a as a carrier signal and the signal from the modulation signal generator 11b as a modulation signal so as to generate a pilot signal to be injected into the feedforward amplifier.
In addition, a reference signal generator 22a of receiving the carrier signal directly outputted from the pilot signal generator 11a to the DSB orthogonal detection circuit 22 is used to down-convert an output signal taken out of a coupler connected between the directional coupler 9 and the output side so as to have a transmission carrier removed by a filter, and results of sampling with the A/D converter are used to output a voltage of controlling the second vector adjustor 7 so that the control circuit 14 surpresses a distortion signal of the feedforward amplifier, that is, the level of the pilot signal becomes the lowest.
While the feedforward amplifier is originally an apparatus of controlling the vector adjustor mainly based on the output signal including the pilot signal and the pilot signal taken out thereof, it is necessary to set a frequency of the pilot signal outside a frequency band of the output signal and so the distortion signal cannot be sufficiently suppressed.
The feedforward amplifier of the above past example generates the pilot signal from the signals of the two oscillators of the pilot signal generator 11a and modulation signal generator 11b, and detects the output signal with the signal of the pilot signal generator 11a. Thus, it is possible to set the frequency of the pilot signal within the frequency band of the output signal so as to suppress the distortion signal under an optimum condition.
In the above configuration, however, there are a large number of the oscillators used to detect generation of the pilot signals, and at least the DSB signal generator 21 needs the pilot signal generator 11a and modulation signal generator 11b. As the oscillators are not small enough to be integrated on an integrated circuit together with other components, they need to have a separate configuration from other circuit components that can be integraded on an intergrade circuit, and this has hindered miniaturization of the feedforward amplifier.
Furthermore, a plurality of oscillators need to be mutually placed with certain spacing in order to secure isolation, and this has further hindered the miniaturization of the feedforward amplifier.
The present invention has been implemented in consideration of the above problems, and an object thereof is to obtain the feedforward amplifier and so on capable of further being miniaturized by reducing the number of the oscillators while suppressing the distortion signal under the optimum condition.
One aspect of the present invention is a feedforward amplifier having:
amplifying means of amplifying an input signal to obtain an amplified signal;
pilot signal generating means, having one local oscillator and a frequency divider for dividing output of said local oscillator, of generating a predetermined pilot signal based on the output of said local oscillator and the output of said frequency divider;
combining means of combining said input signal or said amplification signal with said pilot signal to generate a combined signal;
extracting means of extracting any distortion component from said combined signal;
output signal generating means of removing said extracted distortion component from said combined signal to generate an output signal; and
adjusting means of using any one of the output of said local oscillator, the output of said frequency divider, said pilot signal and said output signal from said output signal generating means to make an adjustment for removing said distortion component.
Another aspect of the present invention is the feedforward amplifier, wherein said pilot signal generating means has modulating means of having the output of said local oscillator modulated by the output of said frequency divider, a frequency of the output of said local oscillator is within a frequency band of the output signal from said output signal generating means, and a frequency of the output of said frequency divider is outside the frequency band of the output signal from said output signal generating means.
Still another aspect of the present invention is the feedforward amplifier, wherein said pilot signal generating means has a first mixer of mixing the output of said local oscillator and the output of said frequency divider, and the frequency of the output of said local oscillator is within a frequency band of the output signal from said output signal generating means, and the frequency of the output of said frequency divider is outside the frequency band of the output signal from said output signal generating means.
Yet still another aspect of the present invention is the feedforward amplifier, wherein said adjusting means performs said adjustment by using said pilot signal and said output signal.
Still yet another aspect of the present invention is the feedforward amplifier, wherein said adjusting means has a first converting means of converting said output signal into a low frequency band which is lower than the original frequency band and a second converting means of converting said pilot signal into a low frequency band which is lower than the original frequency band, and performs said adjustment by using the pilot signal converted into said low frequency band and the output signal converted into said low frequency band.
A further aspect of the present invention is the feedforward amplifier, wherein said first converting means has said local oscillator and a second mixer of combining the output from said local oscillator and said output signal, and said second converting means has said frequency divider and uses the output from said frequency divider as said converted pilot signal.
A still further aspect of the present invention is the feedforward amplifier, wherein said first converting means at least one of a first filter of receiving input of said output signal has provided on a front stage of said second mixer and a second filter of receiving input of said second mixer.
A yet further aspect of the present invention is the feedforward amplifier, wherein said first filter is a band pass filter.
A still yet further aspect of the present invention is the feedforward amplifier, wherein said first filter is a band rejection filter.
An additional aspect of the present invention is the feedforward amplifier, wherein said first filter is a band pass filter of having at least two frequencies pass through it.
A still additional aspect of the present invention is the feedforward amplifier, wherein said second filter is a band pass filter.
A yet additional aspect of the present invention is the feedforward amplifier, wherein said second filter is a low pass filter.
A still yet additional aspect of the present invention is the feedforward amplifier, wherein said second filter is a band rejection filter.
A supplementary aspect of the present invention is the feedforward amplifier, wherein a dividing ratio of said frequency divider is a fraction.
A still supplementary aspect of the present invention is the feedforward amplifier, wherein a dividing ratio of said frequency divider is variable.
A yet supplementary aspect of the present invention is the feedforward amplifier, wherein:
said extracting means has a first branching means of branching said input signal into two to output one of them to said amplifying means and a first opposite phase combining means of receiving the other output of said first branching means and the input of said combined signal and branching said combined signal into two so as to output as said distortion component a signal in which one of branched said combined signal and the other output of said first branching means are combined in an opposite phase and also output the other of said combined signal asxe2x80x94is;
said output signal generating means has a second opposite phase combining means of outputting as said output signal a component in which said distortion component from said first opposite phase combining means and the other of said combined signal are combined in the opposite phase.
A still yet supplementary aspect of the present invention is the feedforward amplifier, wherein said output signal generating means has:
vector adjusting means, provided between said first opposite phase combining means and said second opposite phase combining means, of adjusting an amplitude and a phase of said distortion component; and
distortion component amplifying means, provided between said vector adjusting means and said second opposite phase combining means, of amplifying the output of said vector adjusting means.
Another aspect of the present invention is the feedforward amplifier, wherein at least two of said local oscillator, said frequency divider, said first mixer, said second mixer, said first filter, said second filter and said adjusting means are integrated in the same semiconductor substrate.
Still another aspect of the present invention is a feedforward amplification method having the steps of:
amplifying an input signal to obtain an amplified signal; dividing output of one local oscillator and generating a pilot signal based on the output of said local oscillator and said divided output;
combining said input signal or said amplification signal with said pilot signal to generate a combined signal; extracting any distortion component from said combined signal;
removing said extracted distortion component from said combined signal to generate an output signal;
using any one of the output of said local oscillator, the output of said frequency divider, said pilot signal and said output signal to perform an adjustment for removing said distortion component.
Yet still another aspect of the present invention is a communication apparatus having a feedforward amplifier, transmitting means of performing transmission and receiving means of performing reception.
The present invention as described above uses the local oscillator and the frequency divider to generate the pilot signals, and generates them by mixing them with the mixer so that the number of the oscillators can be reduced and miniaturization of the feedforward amplifier can be implemented.